One of the main targets of LTE (Long Term Evolution) and SAE (System Architecture Evolution) is to reduce call connection delay. A call connection includes two main components of RRC (Radio Resource Control) establishment and call control. For that reason, the point of call connection lies in how efficiently the operations of these two components are carried out. Here, RRC constitutes the core in radio control and has the functions of including mobility control of a terminal (e.g. a command to transfer a base station in connection). Moreover, a call connection is performed in an upper layer node and includes authentication and checking what call is established.
FIG. 1 shows an overview of call connection steps in the conventional (UMTS) scheme. Referring to this figure, in step (hereinafter abbreviated as “ST”) 11, the terminal determines power for transmitting an RRC message to the base station/radio control node and performs layer 1 processing to secure resources for message transmission use. Determination of transmission power is to optimize the power transmitted by a terminal, and the terminal starts transmission to the base station with an initial value determined from received quality of report information and gradually increases power until the terminal receives a response from the base station. The power upon receiving a response from the base station/radio control node or a power with an addition of offset to that power is the power for transmitting an RRC message. Resources for transmission use are secured so as to prevent a plurality of terminals from using the same resources at the same time.
In ST12, based on the power and the resources for transmission use determined in ST11, the terminal transmits an RRC connection establishment request to the base station/radio control node. This request information includes, for example, an identifier for identifying the terminal and the reason for the RRC connection establishment request. The terminal accepts the request and transmits a message to command setup of an RRC connection. This message includes the identifier of the terminal for managing the terminal in the base station/radio control node, and radio resources and channel setup for transmitting the RRC message. After this, the terminal establishes an RRC connection (i.e. a channel setup) and, after the establishment is finished, transmits a response message using the channel that is set up.
In ST13, message transmission and reception are performed mainly between the terminal and the upper layer node. These transmission and reception are performed by including a message for the upper layer node in the RRC message. The details setting up here are the level setting for a service to be provided, mutual authentication between the terminal and the upper layer node and security (encryption and securing confidentiality) settings. Setting up encrypted keys and secret keys is also carried out from the upper layer node to the base station here.
In ST14, in accordance with the service level determined in ST13, the channel setting for actual data transmission and reception, is performed. This includes radio setup between the base station/the radio control node and the terminal and the network resource setup between the upper layer node and the base station/the radio control node. Data communication is started after this.
The call connection steps shown in FIG. 1, for ease of description, “service notification, authentication and security setup” and “channel setup for data transmission and reception” are described completely in serial order, but, considering the response messages, the actual call connection steps are partly entwined. Nevertheless, this is not an essential problem, and the concept is that “channel setting for data transmission and reception” is carried out after “a service notification, an authentication and security setup”. Moreover, the base station and the base control node have been explained as an integrated entity, but they are actually separated as two apparatuses.
In this way, in the call connection steps shown in FIG. 1, respective processing (ramping process in layer 1, RRC connection setup, service notification, authentication and security setup, channel setting for data transmission and reception, etc.) are performed in serial. This makes a call connection time-consuming. Moreover, a channel setup is performed twice in the RRC connection setup and the channel setup for data transmission and reception (see Non-patent Document 1 and Non-patent Document 2). For this reason, the radio channel (layer 1) needs to be set up more than once, which is inefficient.
Then, to solve the above problem, another method of call connection is currently proposed by 3GPP, and the steps of this call connection method are shown in FIG. 2. Referring to FIG. 2, in ST21, the terminal acquires an identifier managed in the base station. This may be layer 3 processing or this may be layer 2 or layer 1 processing.
In ST22, the terminal transmits an RRC connection establishment request to the base station using the identifier acquired in ST21. This is different from the conventional (UMTS) scheme in that this RRC connection establishment request includes “an authentication in the upper layer node and information for a service setup (applicable to a service notification, an authentication and security setting in UMTS).”
In ST23, the base station extracts information for the upper layer node, and in ST24, transmits the extracted information to the upper layer node. Moreover, at the same time, the base station prepares for an RRC connection establishment.
Based on the information “the authentication in the upper layer node and the information for a service setup (applicable to the service notification, the authentication and security setting in UMTS)” transmitted from the base station, the upper layer node authenticates the terminal, determines the service level and makes a preparation for security. Then, in ST25, the upper layer node transmits a response message to the base station.
In ST26, based on the message received by the base station, the base station determines the radio channel for data transmission between the base station and the terminal. Then, the base station creates an RRC message, which sets up an RRC connection and a radio channel for data use, and embeds a message transmitted from the upper layer node into the RRC message, and, in ST27, transmits the message to the terminal.
The terminal sets up the RRC connection and the radio for data use, based on the message received from the base node. Moreover, the terminal sets up security, authenticates the network, and sets up the service level. Communication is started after this.
In this way, in the call connection steps shown in FIG. 2, messages for the base station and the upper layer node are concatenated and transmitted from the terminal. Moreover, a message from the base station is transmitted after the base station waits for a message from the upper layer node.
Non-patent Document 1: 3GPP TR25.331, “Radio Resource Control (RRC) Protocol Specification”
Non-patent Document 2: 3GPP TR24.008, “Mobile radio interface Layer 3 specification; Core network protocols; Stage3”